Lemna lab problems

"KONING,ROSS E. Biology KONING at easternct.edu
Tue Nov 7 11:38:11 EST 2000


Please tell us more about the experimental
setup.  Were the solutions buffered or was
the pH adjusted properly?  Were the containers
closed or open to the air?  Were they placed
in direct sunlight or under fluorescent lamps?

My first guess is that the greenhouse effect inside
a closed container in the greenhouse cooked them...
it is a common mistake.  Closed clear containers
in sunlight are a disaster.  Stick a thermometer 
through the stopper or drill a hole in the wall of
a plastic container and you will find out what 
kills them.

The pH problem can pickle the plant tissue quite
rapidly.  Fertilizer solutions often have an extreme
pH...used in a dilute form on soil they are OK because
of the buffering capacity of the soil.  In a soilless
situation (such as with most Lemna cultures), the
same fertilizer is a pickling agent.

Osmoticum can also be a problem.  If the solution
is too high in total dissolved salts, the plant tissue
is dehydrated and killed. Again, the fertilizer solution
one puts on a well-watered potted plant is diluted
by the water already in the soil; Lemna floated on 
the same strength of solution would be dried out 
very quickly.

Any one of these three killers would work within
minutes to hours and give the symptoms you
described.  Which of these three might be the
cause in your case would have to be investigated
more directly.

Finally, even in open vessels the greenhouse
effect can really kill aquatic plants.  If the surface
of the liquid is almost free of plants, the intense
light penetrating the water can bring the temperature
of a container of water to lethal levels.  Once the
surface is overgrown with floating plants, the water
temperature stays "safe" because of the shading
and the evaporative cooling of the leaves due to
transpiration.  So when I'm doing a "new" tub 
culture of Salvinia or Lemna or Pistia, I try to keep
it shaded until the surface is well-covered.  Then
I move it to brighter light.  You can also do a "nurse"
culture" but then you have separation problems later.
By this I mean putting a Pistia start in an established
tub of Lemna or Salvinia until you have enough Pistia
to cover the surface of a new tub on its own.

Using closed containers under fluorescent lamps
usually avoids the "greenhouse effect."

Good Luck!


Ross E. Koning, PhD
Professor of Biology - Goddard Hall
Eastern Connecticut State University
Willimantic, CT 06226 USA
Pager: (860)-744-2705 (leave return number at beep)
Office: (860)-465-5327
Home: (860)-423-9724
Email: koning at easternct.edu
Home: koningr at snet.net

> ----------
> From: 	E-Ribbens at wiu.edu
> Sent: 	Tuesday, November 7, 2000 10:55 AM
> To: 	plant-ed at hgmp.mrc.ac.uk
> Subject: 	Lemna lab problems
> We're trying a new lab here, population growth using Lemna minor. We've 
> been cultivating it in the greenhouse (it turns out for 22 + years!), but 
> when we set up the growth experiment the thalli promptly all bleached
> white 
> (within two days). The ones left in the dark are the only ones which
> didn't 
> bleach, although they are looking a bit poorly as well. Any idea why? 
> Fluorescent light? Increase in light intensity? Water chemistry change? 
> Just general stubbornness?
> ---


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